First, we should make our problem an equation. What percent is a variable(which we will call P). 'of' identifies that we are multiplying, 300 liters is 300 liters, is identifies the = sign, and 2.7 liters is simply 2.7. Our equation now is P * 300 = 2.7 . We know that our percent must be less than 100% because 2.7 is less than 300.
Now we have a simple algebraic problem. We must divide both sides by 300 to isolate P- P * 300/300 = 2.7/300 .
Now we have cancelled out 300 by our variable, leaving the equation P = 2.7/300. Now we divide 2.7 by 300.
(Using this website's calculator)2.7/300 = 0.009. P= 0.009. The only problem is that this is not a percent.
If you remember, if you have, for example, 50%, and you want to convert it to a decimal, you move the decimal place(currently it is 50.0%) twice to the left(remember, by doing this you are making it hundreths, and percent literally means "per 100". It literally measures what hundreth. This is why 1% of 100 is 1, or 15% of 100 is 15. Better yet, 1% of one is 0.01, or one hundreth).
If we apply this to our problem, we know that we are going the OTHER way- converting a decimal to a percent. Simply move the decimal place in 0.009 twice to the right(like multiplying by 100) and add the percent sign. So our percent is 0.9%.
Now to check(with the handy web2.0calc)- 0.9% * 300 = 2.7
We see that our answer satisfies the equation, and, therefore, P= 0.9%.